1. Field of the Invention
This invention relates to a process for preparing unsaturated aldehydes having three to four carbon atoms by oxidizing the corresponding olefin with molecular oxygen. More particularly, this invention relates to a process for preparing methacrolein in high yields by oxidizing isobutylene with molecular oxygen.
2. Description of the Prior Art
Various processes for preparing unsaturated aldehydes by the catalytic vapor phase oxidation of olefins having three to four carbon atoms with molecular oxygen in the presence of various catalysts have been proposed. In most of these processes, acrolein has been advantageously produced from propylene. However, it has been difficult to prepare methacrolein from isobutylene using similar processes. For example, it is known that acrolein can be prepared from propylene in a selectivity of more than 85 % and an olefin conversion of 90-95 % which is required for industrial production. If the process is used for the preparation of methacrolein from isobutylene, selectivities for methacrolein of up to 50 % are obtained which is unsatisfactory for industrial purposes.
Even though propylene and isobutylene are very similar compounds and isobutylene is readily combustible, there is a substantial difference in the oxidative reactivity of the two compounds. However, it is expected that suitable catalysts can be found which exhibit high yields and selectivities for the conversion of isobutylene to methacrolein.
A need, therefore, exists for a catalyst which will promote the oxidative reaction of isobutylene to give methacrolein in high yields and selectivity.